This invention relates generally to integrated circuits having parallel, spaced arrays of leads and is particularly directed to the mounting and coupling in circuit of two dynamic random access memories of different sizes and having different numbers of leads or pinouts.
An integrated circuit (IC) is an interconnected array of active and passive elements integrated with a single semiconductor substrate or deposited on the substrate by a continuous series of compatible processes. The IC is typically capable of performing at least one complete electronic circuit function. Normally, only the input, output and supply terminals, or pinouts, are accessible, with the various active and passive circuit elements encapsulated in a plastic housing from which the various pinouts extend to facilitate coupling of the IC to other circuitry. The pinouts or leads may be arranged in various configurations, but perhaps the most common pinout arrangement is in the form of a dual-in-line package consisting of a pair of spaced, linearly aligned, parallel lead arrays extending from facing edges of the generally rectangular IC plastic housing.
One type of IC in common use is a random access memory (RAM), which may be either of the dynamic or static type. Static RAMs (SRAMs) are generally of the CMOS type and are characterized in that data stored therein remains in the RAM indefinitely, or at least until power is removed from the static RAM. Dynamic RAMs (DRAMs), on the other hand, require a refresh system for maintaining data in memory, but offer a greater memory capacity at lower cost than SRAMs. Thus, DRAMs are particularly adapted for systems requiring large memory capacities wherein a memory backup is not required.
DRAMs are typically of the dual-in-line type wherein a pair of spaced, parallel, linear pinout arrangements extend from facing lateral edges of a plastic housing. Most available DRAMs have a capacity of either 64 or 256 kilobits and include 16 pinouts extending therefrom. More recently, larger capacity DRAMs have become available which are capable of storing one and even as much as four megabits of data. These larger capacity DRAMs are slightly longer in size, although still of a generally rectangular shape, and are characterized as having 18 leads extending therefrom. Thus, while the 64k and 256k are mutually compatible in terms of mounting and electrical coupling requirements, as are the 1Meg and the 4Meg DRAMs, the larger capacity DRAMs, i.e., 1Meg and 4Meg, are not compatible with those having a smaller memory capacity, i.e., 64k and 256k. Therefore, PC boards designed for use with 64k or 256k DRAMs cannot be upgraded to accommodate the newer 1Meg and larger DRAMs by using the same PC board socket. Thus, different PC boards are required for accommodating different size DRAMs. This situation requires PC board suppliers to maintain larger inventories and limits PC board flexibility in terms of meeting future application expansion.
The present invention is intended to overcome the limitations of the prior art by providing a PC board mounting and coupling arrangement which is adapted to accommodate two IC configurations of different size and having different pinout arrangements within a minimum footprint area on the surface of a PC board.